The present invention relates to an electron gun for providing electrons grouped in short pulses of predetermined pulse repetition frequency f.sub.0.
In many applications, it is necessary to provide electrons grouped in short bunches. This is in particular the case when it is desired to inject these electron bunches into accelerating systems of the high-energy linear type.
The conventional solutions use electron guns with a triode structure formed by an electron-emitting cathode, a grid and an anode, all aligned. The electrons are provided during the times where a gating voltage is applied to the grid, the anode and the cathode being supplied with DC voltages.
A major disadvantage of this approach is related to the gating of the grid during a very short time, for example shorter than a nanosecond. As a matter of fact, the presence of inevitable parasitic capacitances produces in the triggering circuits time constants which are difficult to decrease. If, in addition, as is the case in certain applications, it is desired to obtain electrons grouped in extremely short times, of about 10 to 100 picoseconds, it is necessary to effect a velocity modulation with an additional cavity resonator, which increases the complexity and the cost of the device.